Question

Problem 4: Advanced electrical ceramics overwhelmingly control the global market share (figure 1). One interesting technology that uses electrical ceramics is the non-linear voltage dependent resistor, also termed varistor. The most common material used to make varistors is ZnO. The following questions are related to ZnO varistors. Note that you may need to do some independent research for some of these questions. a) Briefly outline how a varistor works (2 points). b) Describe an application of a varistor (2 points). c) Suppose you are an engineer at a company that produces varistors. Based on what you know from part (a), describe a way that you would increase the breakdown voltage of a varistor part (2 points).

Answer 1

a) brief outline about the way varistors works : it works according to applied voltage its resistance is dependent on voltage. And it has non linear characteristics. at lower value of voltage it shows higher resistance, it has similar characteristic like diode. When we apply small voltage very less current flows as we increase the voltage at certain voltage diode junction breaks and large current starts flowing.

b)

Application of varistor

Varistors are used to protect electric circuits from over voltage, it also used to protect electronic devices. Also protects against lightning and electrostatic discharge.

It provides protection against surges in AC / DC motors.

c) for increasing the break down voltage I will suggest to increase the thickness of varistors or I will decrease the doping in the drift region.